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oh ok! yes, in this section of the book, looks like Gwen is using a UV Hound that was in fact rented from Hilton Kelly's organization Community In-Power and Development Association. Can the world get any smaller...

Hi, just found it interesting when i read about the UV Hound - it's actually not a mass spectrometer but an optical spectrometer not too dissimilar to our kits, but in the UV range. The technique is called Ultra-Violet Differential Optical Adsorption Spectrometer (UV-DOAS) and they said they use Beer's Law just like our activity here: #beers-law

The readout looks really similar to https://SpectralWorkbench.org although it's in a range we can't detect - UV, so down to 200 nanometers (our kits only go down to 400, pretty much same as human vision)

Also it needs to pass through 1000+ feet of open air, and get reflected back in. probably because air is so transparent:

Here's a gas industry video with more info: https://www.youtube.com/watch?v=mMemTf0djaI -- it's about the OPSIS UV-DOAS, which is another product that uses the same technique. But I wasn't able to figure out the price.

The OPSIS site has a nice diagram of how their spectrometer works; it's basically the same as our kits but in UV, with a really long beam path:

They even use the same spectral matching technique as us. But their spectrometers are probably really well intensity calibrated or have a great baseline comparison spectrum and very little noise or drift.

One idea that the article explores is using a fluorescent coating that will glow, so the camera doesn't have to detect DUV, but can photograph the coating:

Another method involves coating the substrate with a wave-shifting coating such as Metachrome II or various phosphors. These coatings fluoresce in the visible portion of the spectrum. The fluorescence signal can traverse the substrate more easily than short-wavelength UV and, therefore, is detected. The disadvantage is that half the light generated by the fluorescence process radiates away from the sensor and is never detected. The coatings also degrade the MTF of the camera system and can introduce image-retention issues if the camera is running at a high frame rate.

And the lenses have to be made of quartz:

Standard glass lenses will not work well in the deep-UV band, since the typical lens glass absorbs strongly below 300 nm. Special lenses made with quartz (fused silica) or calcium fluorite are required. There are few off-the-shelf sources for these lenses, and the cost is quite high compared to visible-light optics. Microscope objectives are available for confocal microscopes operating in the DUV band.

I think the takeaway is that searching for a price for the OPSIS, or pricing for a different UV-DOAS device that could substitute for the UV-Hound, could get you a moderately lower price, BUT the need for an expensive Deep UV (DUV) camera sensor and lenses makes this device reasonably expensive to start with.

BUT, for those interested in DIY spectrometry for UV, there are some experiments at #uv-imaging, but this hobby imagery website also has a good overview, saying some off the shelf cameras can actually photograph down to 200 nanometers:

a really really powerful Xenon spotlight, aimed across a thousand feet of open air

reflected back with a first-surface mirror

bounced off of a reflective diffraction grating in a dark box like one of our spectrometers

aimed at a CMOS camera OR a spinning mirror plus a UV sensor

wait a long time to get a long exposure

then do it again when there is suspected benzine and other PAHs, kind of like in this post (image below)

I think it's a pretty tough challenge, and you'd have to try to separate out just the benzene detection from any other things you detected, just like we struggled to ID fluorescence spectra in a mixed sample of liquid.

I wonder how the Hound is used if it needs a reflector to bounce the beam back. maybe you have to be on 2 sides of a site? You can be 1000' or more away, but it has to get back to the sensor again somehow.